The present invention relates generally to imagers having a focal plane array of infrared detectors and charge coupled device signal processing circuitry associated with the detectors to transfer the signals produced by the detectors into data processing apparatus where the image may be reconstructed from the signals in a manner determined by the particular mode of scanning employed. Imagers of this general type are disclosed, for example, in the following U.S. patents:
B. k. weimer, U.S. Pat. No. 3,683,193 PA0 Y. takamura, U.S. Pat. No. 3,777,061 PA0 D. r. collins, U.S. Pat. No. 3,771,149 PA0 K. nummedal, U.S. Pat. No. 3,883,437.
In the prior art, of which the foregoing patents are typical, efforts to integrate the photodetectors of such an array with a charge coupled circuitry have in the past led either to hybrid devices wherein the detectors were mounted on top of a separate semiconductor substrate in which the charge coupled circuitry was contained or to an arrangement wherein the photodetectors were formed as portions of the same semiconductor substrate containing the charge coupled circuitry.
The device disclosed and claimed in our copending application Ser. No. 614,277 represents a successful monolithic integration of the detector and its associated CCD circuitry into one efficient and low-cost device.
In the fabrication of our earlier structure disclosed in Ser. No. 614,277, an epitaxial layer is formed on an IR detector substrate and then a portion of that epitaxial layer is etched away as to permit infrared radiation to impinge on the individual detectors of the substrate. This produces charges which are then read out by direct injection into the charge coupled device which is built on the epitaxial layer and functions to transfer charges through the epitaxial layer and into the output of the device. We believe that our invention disclosed and claimed in the aforementioned patent application represents truly significant advances in this art as explained in detail in said application. Our present invention extends the developments in this area of technology and has the further advantage of eliminating the need for removing a portion of the epitaxial layer. Moreover, through the use of a buried layer/surface layer combination, this structure further improves the transfer efficiency of charges from the detector to the charge coupled device thereof and the "fill factor" of the detector.